This invention relates to a process for producing a radiation curable adhesive tape.
Pressure sensitive adhesive tapes have been produced conventionally by coating an adhesive composition prepared by dissolving a natural rubber, a synthetic rubber, or the like in an organic solvent on a substrate made from paper, plastic film, or the like, drying and winding up the substrate on a reel.
But, from the recent demands for saving resources, saving energy and preventing environmental pollution, there has been studied the use of solventless adhesive compositions. As one example of such solventless adhesive compositions, a radiation curable pressure sensitive adhesive has been noticed. This is because the radiation curable pressure sensitive adhesive does not contain an organic solvent principally, that is, to make solventless becomes possible, or even if contained, in a very small amount, and further there are the following advantages in that (1) since radiation which is active energy rays is used, crosslink (polymerization) is fast, (2) since the curing reaction only proceeds when exposed to radiation, the life to use can be controlled freely, and (3) no large drying furnace is necessary during the production of adhesive tapes.
For example, Japanese Patent application Kokai (Laid-Open) No. 10667/82 discloses an adhesive tape obtained from a compound having a vinyl group and a polyfunctional thiol compound, and having good cured properties by exposure to radiation and high cohesion and adhesive properties. Good adhesive properties seems to be resulted from high sensitivity of the SH group in the polyfunctional thiol compound to radiation and competition of the reaction between the vinyl group and the SH group and the chain polymerization-like reaction of vinyl groups each other, which results in making the distance between crosslinking points of cured product longer, and forming rubber-like structure. But in the case of such an adhesive composition containing a thiol compound, even if sufficiently cured by radiation, there remain an unpleasant odor specific to the thiol compound; this is a problem to be solved.